1. Field of the Invention
The present invention relates to a bistable magnetic element which is compact and has high sensitivity and high response speed and a method of manufacturing such a bistable magnetic element. The bistable magnetic element of the present invention is suitable for use in magnetic sensor switches such as a proximity switch and a digital magnetic switch which are used in input devices for computers and information equipment and in equipment for factory automation (FA), and is also suitable for use in digital magnetic memory cells and the like for computers and information equipment which allow high speed read/write operation.
2. Description of the Related Art
With the progress of micro-nano electronic technology and multimedia technology, computers, portable information terminals, AV equipment, FA equipment, measuring/control equipment, etc., have been improved to reduce their sizes and improve their performances. Especially, in the field of computer-related equipment, such trend is remarkable. In magnetic recording devices, such as a hard disk and a floppy disk drive, which serve as external storage devices, it is also desired to realize a storage device which does not have any mechanical moving portion and which makes it possible to carry out read/write operation electronically. An example of such a storage device is an NDRO (non-destructive read-out) magnetic memory card such as a magnetic flash memory card.
In order to meet the demand, micro-sized digital memory cell is necessary which has high sensitivity and high response speed and which has a simple shape and a desired sensor function. However, magnetic elements which satisfy the above-described requirements have not yet been developed.
In the past, a parametron element was used as a non-destructive magnetic memory. However, in such an element using a ferrite core, the rise time of parametric excitation upon reception of a trigger pulse is long (i.e., a few microseconds), and coils are required, which makes it difficult to fabricate the parametron element as a part of an integrated circuit. Accordingly, the parametron element is not used in these days.
After that, a twistor memory element in which electrically conductive permalloy foil is wound helically has been invented. Although the twistor memory element operates as a bistable magnetic memory, the manufacture thereof is troublesome, and it is necessary to supply a large current to the memory element. In addition, the twistor memory element is also difficult to fabricate as a part of an integrated circuit. Due to these drawbacks, the twistor memory element is not used in these days.
Meanwhile, a huge number of magnetic type proximity switches are used in keyboards and mice for computers and word processors, joy sticks for game machines, and proximity sensors for FA. However, a combination module of a Hall element or MR element and a hysteresis comparator used in the magnetic proximity switches requires a magnetic field of a few tens gausses or higher to operate, which means that the sensitivity of the module is low. Moreover, the temperature characteristics of the module is not stable.
A head including a fluxgate sensor can be used to obtain high sensitivity. However, due to demagnetizing fields, the size of the head cannot be reduced. Also, the response speed of the head is low because the head is excited by coil current.